Not applicable.
1. Field of the Invention
The present invention relates to a transaxle apparatus which transmits compound power of driving output and steering output from two respective transmissions to a pair of axles through a differential gear unit. Especially, it relates to the differential gear unit having planetary gearings which is applicable to such a transaxle apparatus.
2. Background Art
A well-known conventional system for driving and steering left and right axles for wheels or sprockets of tracks, which employs a pair of hydrostatic transmissions (xe2x80x9cHSTsxe2x80x9d) provided for the respective axles, is disclosed in U.S. Pat. No. 4,782,650 or Japanese Laid Open Gazette No. Hei 2-261,952, for example. Output rotary speeds of the two HSTs are equalized for straight driving of a vehicle and made different from each other for steering of it.
The conventional system has the problem that the equalization of output rotary speeds between the two HSTs must be precise and if there is difference of capacity between the two, a vehicle is steered differently between leftward and rightward cornering.
The present invention includes an axle driving and steering system including two HSTs and a differential unit. In this regard, one of the HSTs (a driving HST) interlocks with a speed changing operation tool such as a lever or a pedal and transmits power from an engine into the differential unit so as to drive left and right axles forwardly or reversely. The other HST (a steering HST) interlocks with a steering operation tool such as a steering wheel and transmits its output rotational force correspondingly to the direction and degree of the steering operation tool into the differential unit so as to differentially drive the axles.
As one of differential units applicable for such an axle driving and steering system having the two HSTs, there is a differential gear unit having planetary gearings (hereinafter, xe2x80x9ca planetary differential gear unitxe2x80x9d). On the assumption that this planetary differential gear unit is used, an integral transaxle apparatus may be structured in such a manner that the two HSTs and the planetary differential gear unit are disposed together in a common housing. For minimizing such a transaxle apparatus, the planetary differential gear unit should compact and, if possible, simple so as to reduce the number of parts and its manufacturing cost and to ease its assembly and disassembly.
However, for example, the conventional planetary differential gear unit is provided on its both opposite outer sides with ring gears to receive power from the steering HST, and bearings must be provided thereon for locating and journalling the ring gears. Also, bolts, bushes and the like are required to support planet gears on carriers. Thus, the conventional planetary differential gear unit requires many parts for its assembly so as to increase costs and complicate its assembly and disassembly for maintenance, and has a considerably great length in its axial direction.
An object of the present invention is to provide an excellently minimized and simplified transaxle apparatus, which transmits compound power of driving output and steering output from two respective transmissions (especially, HSTs) to a pair of axles through a differential having planetary gearings, wherein the differential gear unit is compact and simple so as to reduce its manufacturing cost and ease its assembly and disassembly for maintenance.
To attain the object, the differential is constructed as follows:
A common center gear serves as a driving input gear which receives the driving output power from a driving transmission. The center gear interlocks with at least one sun gear. A pair of carriers are fixedly disposed around the respective axles oppositely to each other with respect to the center gear. Two groups of planet gears are pivoted on respective carriers and engage with the at least one sun gear. A pair of ring gears serving as steering input gears which receive the steering output power from a steering transmission are supported by the respective carriers. Two oppositely rotating forces are generated from the output power of the steering transmission and transmitted into the respective ring gears. Each group of the planet gears supported by each carrier receive both the rotational force of the sun gear and the rotational force of the ring gear supported by the carrier so as to revolve together with the carrier around the at least one sun gear.
Since each of the ring gears as steering input gears is supported by each of the carriers, the present differential gear unit requires no bearing which has been arranged on the outside of the conventional differential gear unit for locating and rotatably supporting the ring gear, thereby being minimized in its axial direction and reducing the number of parts for assembly thereof.
Preferably, each ring gear is rotatably supported around each carrier in such a manner that the inner peripheral surface of the ring gear slidably abuts against the outer peripheral surface of the carrier, so that the present differential gear unit requires no bearing to be interposed between the ring gear and the carrier, thereby making it further possible to reduce the number of parts for assembly thereof and to be minimized.
Furthermore, each of the ring gears is also supported by each group of the planet gears pivoted on each carrier, thereby securing the support of the ring gear without another part.
This support of ring gear by the planet gear is established by a gear arrangement provided for power transmission between the ring gear and the planet gears. In this regard, each ring gear is integrally formed at its inner peripheral surface with an internal gear to engage with each group of planet gears pivoted on each carrier. Therefore, the rotational forces inputted into the respective ring gears are transmitted through the planet gears and the carriers to the respective axles so as to accelerate one of the axles and decelerate the other, thereby enabling the vehicle to turn left and right. Each ring gear is located and. rotatably supported further securely by both the entire round outer surface of carrier and the engaging portion of the planet gear to the internal gear without another support part.
Furthermore, the internal gear formed on an area of the inner peripheral surface of the ring gear is axially offset from another area thereof rotatably arranged around the carrier. The teeth of the internal gear are centripetally extended so as to locate their tips nearer to the axis of the ring gear than the other inner peripheral surface of the ring gear rotatably arranged around the carrier. In other words, the internal gear forms a step in th ring gear for location of the carrier.
Therefore, the teeth of the internal gear face one of the side surfaces of the carrier, thereby easing the location of the carrier and avoiding the tilt and escape of the carrier in the ring gear.
Both opposite side surfaces of the center gear face the side surfaces of the internal gears of the ring gears, respectively, thereby restricting the motion of the ring gears along the respective axles toward the proximal ends of the axles.
Furthermore, a housing containing the differential gear unit is disposed close to the outer side surface of each carrier, thereby restricting each ring gear to move along each axle toward the distal end of the axle.
For the support of the planet gear on the carrier, each carrier is integrally formed with at least one gear support portion. The at least one planet gear is rotatably supported by the at least one gear support portion so as to engage with the sun gear. The carrier may be integrally formed with at least one projection along the axis of the carrier, thereby serving as the at least one gear support portion.
Due to this structure, the planet gears can be rotatably supported directly by the respective carriers without any other parts such as bolts and bushes, thereby easing the assembly and disassembly of the differential gear unit for maintenance and reducing the number of parts and costs for its assembly.
The above mentioned differential gear unit may be disposed together with the driving transmission and the steering transmission in a common housing, thereby providing a compact integral transmission apparatus.
These and other objects of the invention will become more apparent in the detailed description and examples which follow.